Cascaded removable media data storage system

ABSTRACT

A cascaded removable media data storage system includes a first level enhanced removable media data storage system controller connected to a host or server computer network. Connected in parallel to the enhanced first level removable media data storage system controller are at least two enhanced second level removable media data storage system controllers. Each enhanced second level removable media data storage system controllers is connected to a mirrored group of removable media data storage units.

FIELD OF THE INVENTION

[0001] The present invention pertains to secondary or back-up datastorage systems for individual computers or computer networks; moreparticularly, the present invention pertains to an improved data systemfor secondary or back-up storage of data on removable media such as tapecartridges.

BACKGROUND OF THE INVENTION

[0002] Computer Data Storage

[0003] Computer data storage which is co-located with a host, server, oran individual computer is placed in a section of computer memorydesignated primary storage. This primary storage provides the computerwith the capability to process program instructions, to store inputdata, to retain statements from programs undergoing processing, toretain and use data produced by programs undergoing processing, and toformat data in preparation for output.

[0004] Initially data which goes into the computer is held in primarystorage until the data is used during the processing of programinstructions. During processing of the data by the computer, the primarystorage is used to store the intermediate and final results of allarithmetic and logical operations. Intermediate results are temporarilyretained in storage areas which are often referred to as workingstorage. Working storage areas are specifically set aside for thetemporary storage of data while a program is being run on one or morecomputers. While the computer is running the program and using the data,the computer may be acting as if all program instructions and neededdata are resident in its main memory; however, the program instructionsand data may actually be located miles away at another location anddownloaded into the computer as if resident in the computer's primarystorage. Such storage configuration is called virtual storage. The finalresults from the running of a computer program are transferred tostorage areas that have been designated by the program instructions.These final results will remain at the designated storage areas untiloutput operations begin.

[0005] In addition to storing the data involved in processing, theprimary storage of a computer must retain the program instructions usedfor processing data. As computer applications have become moresophisticated, the size of computer programs has grown exponentially.Such exponential growth in the size of computer programs hasnecessitated the use of virtual storage of computer programs or data inlocations away from the host or server computer to enable sufficientspace in primary storage to run other large computer programs.

[0006] For example, a large international bank may have a designatedtime each day to consolidate all of the transactions from its branchesaround the world. Once this daily consolidation has taken place, themassive amount of consolidated data must be stored somewhere for lateruse in putting together periodic account statements and to provide thespecialized reports necessary to meet regulatory and tax requirements.Such specialized reports could not be run unless the bank's computer hadaccess to large virtual data storage capacity.

[0007] Secondary or Back-Up Data Storage

[0008] Because of the ever growing need for data storage capacity toservice larger and larger computers which run larger and largerprograms—all of which produce massive amounts of data—the need hasarisen for larger and more sophisticated secondary or back-up datastorage systems. Secondary data storage provides a computer system withgreater data processing potential because it expands the amount ofavailable storage space to a computer or a computer network for holdingdata. The data contained in secondary or back-up data storage may be toolarge to be held in primary or working storage; however, to allow theprogram resident in the host or server computer network to run, datastorage space must be located and made available to the host or servercomputer as quickly as possible for data writing and data readingoperations. By providing a host or server computer network with largeamounts of secondary or back-up data storage capacity, the operationalcapabilities of individual computers or a computer network can bemaximized.

[0009] Removable Media

[0010] One of the most used forms of secondary or back-up data storagedevice hardware is a removable media data storage unit. While slower andpossibly more cumbersome than other types of secondary data storage,removable media data storage units such as tape cartridges remain aviable and frequently used data storage option because of its low costand acceptance around the world.

[0011] Because of the way data is actually placed on one or moreindividual removable media data storage units, a removable media datastorage system includes a controller to govern its operation. Theremovable media data storage system controller is used to dividecomputer programs and associated data into sections to guide the databeing written onto one or more removable media data storage units fromthe host or server computer network to an individual removable mediadata storage unit. Such guidance from the removable media data storagesystem controller as to the path by which data is written on one or moreindividual removable media data storage units should be invisible to thehost or server network. Rather, all the host or server computer networkneeds to retain is a “volume number” designating the location of thestored data. The term “volume number” actually comes from early magnetictape data storage systems where a volume number was the identificationnumber of a single reel of magnetic tape. Presently, a “volume number”may identify a single removable media data storage unit or a group ofremovable media data storage units where data is written to or readfrom.

[0012] When stored data is to be read back to one or more computers in anetwork of host or server computers, the removable media data storagesystem controller retrieves the stored data from the one or moreremovable media data storage units where it is actually stored andsupplies the stored data to the host or server computer as if the datacame from a single volume number location.

[0013] Data Storage on Multiple Removable Media Units

[0014] Because one of the problems in reading and writing data ontoindividual removable media data storage units is the lack of speed inthe sequential access of data , the speed of either writing to orreading from secondary or back-up data storage on a removable media datastorage unit has been greatly increased by the use of mass removablemedia data storage systems such as mass tape cartridge data storagesystems which employ strips of magnetic tape in an ordered array. Inthese mass tape cartridge data storage systems, any data recorded in atape cartridge can be accessed directly without having to search theentire contents of the tape cartridge.

[0015] In many removable media data storage systems, data is stored by aprocess known as striping. In striping a serial or linear sequence ofgroups or bytes of data is downloaded by parallel data groups intoparallel groups of individual removable media data storage units. (Inearly magnetic tape data storage systems, bytes of data were writtensequentially in a serial manner onto a single roll of magnetic tape. Thesingle roll of magnetic tape then had to be either wound or unwound togain access to the correct length of magnetic tape holding the neededdata to read the needed data back into the computer.) Thus, if sevenindividual removable media data storage units are available for datastorage, data can be written to storage on the removable media datastorage unit or read from storage on the removable media data storageunit in groups of seven stripes.

[0016] Access to groups of individual removable media data storage unitsis typically accomplished by the use of robotic control or a robot. Theremovable media data storage system controller directs the robot to thegroup of individual removable media data storage units on which data iswritten to or read from. The robot then locates the appropriate group ofindividual removable media data storage units designated by theremovable media data storage system controller for proper storage orretrieval of data. While the data may be written to or read from a groupof individual removable media data storage units, the host or servernetwork sees the data being written to or read from the removable mediasecondary or back-up data storage facility as being written to or readfrom a single virtual volume designated by single volume number or asingle volume number including the location of a group of individualremovable media data storage units. The formulation of the singlevirtual volume designation is accomplished by the removable media datastorage system controller.

[0017] Commonly available removable media data storage systems orremovable media data storage libraries include 15 removable media datastorage units. This library of 15 removable media data storage units maybe configured into two sets of seven removable media data storage units(with a spare in case a removable media data storage unit is out forservice or cleaning). Sets of seven removable media data storage unitsare configured by the removable media data storage system controller toappear to a host or server in a computer network as a single volumenumber. Some manufacturers have found that as few as five removablemedia data storage units can be configured together so that a computerin a host or server network will still see the group of five removablemedia data storage units as a single volume number.

[0018] To increase secondary data storage capacity on removable mediadata storage systems, such as magnetic tape cartridge data storagesystem attempts have been made to serially connect together a string ofmass magnetic tape cartridge data storage systems I, II, . . . , n asshown in FIG. 1. While additional secondary magnetic tape cartridge datastorage capacity can be provided by this serial connection of magnetictape cartridge data storage systems, the serial connection causes otherproblems to arise. Specifically, the serial connection S between themass magnetic tape cartridge data storage systems limits access to otheron-line magnetic tape cartridge data storage systems so that only onemass magnetic tape cartridge data storage system can be written to orread from at anyone one time. Thus, while a write operation or a readoperation is taking place on one mass magnetic tape cartridge datastorage system on the serial connection S, the remainder of the massmagnetic tape cartridge data storage systems on the serial connection Sare rendered unusable.

[0019] Other Secondary Data Storage Systems

[0020] In addition to magnetic tape cartridge data storage, there areother systems associated with the secondary storage of computer data.Such other systems include compact disks (often called CD-ROM's),magnetic disks, magnetic drums, data cells, optical memory data storagesystems, magnetic bubble data storage systems, laser storage systems,holographic data storage systems, optical scanners, printers and storagemedium changers. A group of these secondary data storage systems hasbecome known in the industry as a Redundant Array of Independent DataStorage Devices or a RAID. A numeral suffix indicates the number of datastorage devices available, e.g. RAID3. Each individual storage devicewithin a RAID is identified by its own Logical Unit Number or LUN foraddress purposes.

[0021] Many individual secondary data storage systems have operationalprotocols that are significantly different than the operationalprotocols used to store data on other individual secondary data storagesystems. For example, the output of a typical magnetic tape cartridgedata storage controller will not permit writing data to or reading datafrom anything other than magnetic tape. Other types of more advancedsecondary storage systems are able to write data into storage or readdata from storage in any format and therefore are completely compatiblewith and will accept data passed through a system using another storagemedium. Some in the industry have referred to a RAID or a grouping or anarray of data storage devices with shared data storage capacity as aStorage Area Network.

[0022] Demands on Removable Media Secondary Data Storage Systems

[0023] In addition to providing a large amount of secondary data storagecapacity on removable media data storage units, there are still otherrequirements that are placed on secondary data storage systems which useremovable media data storage units. Such other requirements include: (a)back up secondary data storage capacity, (b) recreation of secondarydata storage, and (c) fault tolerance or the ability to provide alocation for data storage should one or more individual removable mediadata storage units become inoperable or unavailable when the data is tobe written on or read from one or more removable media data storageunits. One method of meeting the need for backup secondary storagecapacity, the need to recreate secondary data storage and the need forfault tolerance is to provide a second, redundant, identical array ofdata storage capacity. The process of providing a second, redundantarray of data storage capacity is known in the industry as “mirroring.”To prevent unforseen occurrences such as power failures, fires,earthquakes, storms, or sabotage from interfering with the writing onand reading from removable media data storage unit, such mirroredremovable media data storage units may be located thousands of milesapart.

[0024] Finally, there is the ever present demand for greater speed inboth writing data to storage and reading data from removable media datastorage units to meet the requirements of newer computers that canprocess data at ever increasing speeds. To meet the demand for greaterspeed in both writing data to and reading data from removable media datastorage units, removable media data storage units must be both able tophysically transfer data faster to and from removable media data storageunits as well as provide increased availability of those removable mediadata storage units not in use.

SUMMARY

[0025] The cascaded removable media data storage system of the presentinvention provides the following advantages:

[0026] i) increased back-up or secondary data storage capacity;

[0027] ii) greater fault tolerance; and

[0028] iii) increased speed for both writing data to back-up storage andreading data from secondary back-up storage.

[0029] The foregoing advantages are provided by arranging a system ofremovable media data storage system S libraries into a cascade. Byconnecting the removable media data storage system controller of one ormore removable media data storage units together into a cascade, theentire cascaded data storage system provides the supported computernetwork with increased data storage capacity, enhanced performance, andbetter availability of storage system capacity in the event of a datastorage fault (fault tolerance).

[0030] In its preferred embodiment, the basic removable media datastorage system of the present invention includes three, fivechannel-removable media data storage system controllers. The first levelfive channel-removable media data storage system controller is linkeddirectly to the host or server computer network and then configured foreither a mirrored array or RAID data transfer to secondary data storage.Two second level five channel-removable media data storage systemcontrollers are each attached to a backend channel of the first fivechannel-removable media data storage system controller. One or moreremovable media data storage units is connected to each of the twosecond level five channel-removable media data storage systemcontrollers.

[0031] Both the first level and the second level five channel-removablemedia data storage system controllers allow for full operational speedof the removable media data storage system with little or no memorybuffering for temporary storage of data during either the data writingor data reading process. In addition, each of the five channel-removablemedia data storage system controllers provides for the virtualizing ofthe commands which provide for multiple operation of the removable mediadata storage units. For example, the control of the robot by the secondlevel removable media data storage system controller actually connectedto one or more removable media data storage units being used must appearto be a single robot to the first level removable media data storagesystem controller which is connected to the other second level removablemedia data storage system controller. All of the second level removablemedia data storage system controllers connected to the removable mediadata storage units must make it appear to the first level removablemedia data storage system controller as if but one robot were inoperation.

[0032] In alternate embodiments of the invention, other RAID's may beused together with the basic removable media data storage system. Instill other alternate embodiments of the invention, additional removablemedia data storage units may be added to the basic removable media datastorage system.

DESCRIPTION OF THE DRAWINGS

[0033] A better understanding of the cascaded removable media datastorage system array of the present invention may be had by referencesto the figures wherein:

[0034]FIG. 1 is a schematic representation of a prior art magnetic tapecartridge data storage system utilizing a serial connection;

[0035]FIG. 2 illustrates the symbology used in the following drawingfigures to designate a removable media data storage unit;

[0036]FIG. 3 is a schematic representation of the basic cascadedremovable media data storage system of the present invention;

[0037]FIG. 4 is a schematic representation similar to FIG. 3 includingadditional removable media data storage capacity on one side of thesystem;

[0038]FIG. 5 is a schematic representation of the cascaded removablemedia data storage system of the present invention including additionalremovable media data storage capacity on both sides of the system;

[0039]FIG. 6 is a schematic representation of the basic cascadedremovable media data storage system of the present invention including athird mirrored group of removable media data storage units;

[0040]FIG. 7 is a schematic representation of a cascaded storage systemarray similar to that shown in FIG. 6 with additional removable mediadata storage capacity added to the third mirrored group of removablemedia data storage units;

[0041]FIG. 8 is a cascaded data storage system array similar to FIG. 6with a fourth mirrored group of removable media data storage units;

[0042]FIG. 9 is a cascaded data storage system similar to that shown inFIG. 8 with additional removable media data storage capacity added tothe third mirrored of removable media data storage units;

[0043]FIG. 10 is a cascaded data storage system similar to that shown inFIG. 8 with additional removable media data storage capacity added toboth the third and fourth mirrored of removable media data storageunits;

[0044]FIG. 11 is a cascaded data system storage similar to that shown inFIG. 8 including a fifth mirrored group of removable media data storageunits;

[0045]FIG. 12 is a cascaded data storage system similar to that shown inFIG. 11 with additional removable media data storage capacity added tothe third mirrored group of removable media data storage units;

[0046]FIG. 13 is a cascaded data storage system similar to that shown inFIG. 11 with additional removable media data storage capacity added toboth the third and fourth mirrored groups of removable media datastorage units; and

[0047]FIG. 14 is a cascaded data storage system similar to that shown inFIG. 11 with additional removable media data storage capacity added tothe third, fourth and fifth mirrored groups of removable media datastorage units.

DESCRIPTION OF THE EMBODIMENTS

[0048] Purpose of the Invention

[0049] The purpose of the cascaded removable media data storage systemof the present invention is to increase data transfer rates both to andfrom one or more removable media data storage units, to increase thestorage capacity of a secondary or back-up network of removable mediadata storage units, and to increase the fault tolerance of a removablemedia data storage system. The disclosed cascaded removable media datastorage system of the present invention is completely independent of thehost computer system and does not rely on any particular host computernetwork system architecture to be operational. Further, the disclosedcascaded removable media data storage system is completely stand aloneas it does not rely on any outside command or control.

[0050] General Description

[0051] In a general sense, the present invention includes removablemedia data storage system controllers with added or enhancedcapabilities that are connected together in a variety of cascades toachieve a highly fault tolerant removable media data storage system thatfeatures high performance, high capacity and high fault tolerance.Independent groups of removable media data storage units or othersecondary or back-up data storage systems may be added to the basiccascaded removable media data storage system of the present invention tofurther increase the capacity of the data storage system.

[0052] Problems to be Solved

[0053] To enable the operability of the cascaded removable media datastorage system of the present invention it was discovered that thefollowing problems had to be solved.

[0054] i) Command delays from one removable media data storage systemcontroller to another;

[0055] ii) Virtualization of robotic commands—even though there may bemore than one removable media data storage medium changer, all mustappear as just one to the host or server computer network; that is, acommand sent to a removable media data storage medium changer must causeall removable media data storage medium changers to execute thatcommand;

[0056] iii) Virtualization of slots in the removable media data storagemedium changers—the removable media data storage controller must be ableto group removable media data storage units together so that when a newvolume is requested by the host or server computer network, the correctseries of removable media data storage units are loaded together in theproper sequence to make the group of removable media data storage unitsappear as but one removable media data storage unit to the host orserver computer network.

[0057] Enhanced Removable Media Data Storage System Controllers

[0058] Accordingly, in general, the enhanced removable media datastorage system controllers which implement the cascaded removable mediadata storage system of the present invention each have the capabilityto:

[0059] i) Reduce command delays from one removable media data storagesystem controller to the next;

[0060] ii) Virtualize robotic commands for removable media data storageunits; and

[0061] iii) Virtualize slots in the removable media data storage mediumchanger.

[0062] More specifically, each removable media data storage systemcontroller must be aware of whether or not it is connected to anotherremovable media data storage system controller, and it must notinterfere with the operation of the cascaded removable media datastorage system as a whole. Each removable media data storage systemcontroller need not be able to fully communicate with another connectedremovable media data storage system controller in the cascade. Forexample, in a pass-through mode, when a removable media data storageunit is in use, such in-use information would be passed upward throughthe second level removable media data storage system controller througha first level removable media data storage system controller to the hostcomputer. To accomplish this pass-through of in-use information theremovable media data storage system controllers must be aware of theirposition in the cascade. That is, a removable media data storage systemcontroller must be aware of whether it is in a first level position or asecond level position in a cascade. Since the host computer eitherwrites to or reads from one or more individual removable media datastorage units, the signal sent to or received from the one or moreremovable media data storage units is virtualized to appear to the hostcomputer as a single volume number. Therefore, the removable media datastorage system controller must be able to virtualize certain commandsfrom a host or server computer network directed to removable media datastorage units such as a “Request Element Status” command.

[0063] For example, when a “Request Element Status” command is sent bythe host or server computer network to one or more removable media datastorage units, the removable media data storage system controllervirtualizes the seven tape sets in a fifteen tape configuration, so thatthe host computer sees only seven slots, not fifteen. Further, when thehost or server computer network tells the removable media data storagesystem controller to “Load Set One”, the removable media data storagesystem controller knows independently of the host computer whatindividual removable media data storage units are included in Set One.Therefore, while the host computer expects that its instruction to “LoadSet One” loads a removable media data storage unit into a data reader ora data writer, the first level removable media data storage systemcontroller in the cascade will be passing this instruction on to thesecond level removable media data storage system controllers. The secondlevel removable media data storage system controllers will now directthe robotic control to load a set of removable media data storage unitswithin the removable media library into the data readers or data writersand then report this event back up through the second level and thefirst level removable media data storage system controllers to the hostor server computer network. The second level and the first levelremovable media data storage system controllers will virtualize the setof removable media data storage units that has been loaded into the datareaders or data writers to appear to the host computer as “Set One”,irrespective of the actual individual removable media data storage unitson which the data is stored.

[0064] Basic Cascade

[0065] By specific reference to the basic cascaded removable media datastorage system 100 shown in FIG. 3, when the first level removable mediadata storage system controller 110 connected to the host computer 20receives a command from the host computer 20 it can pass the commanddown the left side 100A of the cascaded data storage system 100 or theright side 100E of the cascaded data storage system 100 depending on theimbedded rule set within the removable media data storage systemcontroller 110. The data will end up following a path to a configurationof removable media data storage units 140.1 or 140.2 adequate to meetthe data storage write or read requirements of the host or servercomputer network 20. Such path could be a fault tolerant pathestablished because of a hardware or software malfunction or it could bea mirror split to an identical configuration of removable media datastorage units in another branch of the system. If desired, the commandfrom the host computer 20 may be passed through the first levelremovable media data storage system controller 110 to a tape compatible,for example, RAID or through one of the two second level removable mediastorage system controllers 120, 130 to a tape compatible RAID connectedto one of more of open channels A, B, or C extending from each of thesecond level removable media storage system controllers 120, 130.

[0066] In the preferred embodiment of the basic cascaded removable mediadata storage system 10 of the present invention, it was found thatcertain features had to be added to all of the removable media datastorage system controllers 110, 120, and 130 to make the cascadedremovable media data storage system 10 of the present inventionoperational. These added features were built around removable media datastorage system controllers 110, 120, and 130 which have five channels A,B, C, D, and E. These five channels allow for the removable media datastorage system controllers to have a mirrored set of removable mediadata storage units 140.1 and 140.2 and a redundant fault tolerance datastorage system. Such configuration is known as a 2+1 RAID 3 data storagesystem. In a 2+1 RAID 3 data set the first level removable media datastorage system controller 110 appears as two data storage devices to thehost computer, not just one. Therefore, according to the presentinvention, it is possible for a removable media data storage systemcontroller to support not only a mirrored configuration of removablemedia data storage units, but by using its three remaining channels, itcan support a 2+1 RAID 3 data storage system. The basic cascadedremovable media data storage system 100 shown in FIG. 3 is a singlelevel cascade which features two mirrored sets of removable media datastorage units 140, 140.1, 140.2, schematically shown in left and rightbranches 100A, 100E in FIG. 3, and accessibility to three RAID sets withjust three removable media data storage system controllers 110, 120, and130. This basic single level cascade 100 gives the host computer 20access to seven volumes of removable media data storage with just threeremovable media data storage system controllers 110, 120, and 130;rather than access to seven volumes of removable media data storage withseven removable media data storage system controllers according to theserial configuration depicted in FIG. 1.

[0067] Alternate Embodiments

[0068] In FIG. 4 is shown a second embodiment 200 of the cascadedremovable media data storage system of the present invention. Allcomponents and the relative positions of those components within thecascade 200 have similar reference numbers to those shown in FIG. 3except that the reference numbers include a “2” in the hundreds place.Added to the second level removable media data storage system controller220 on the left side 100A of the cascade 200 is an additional set ofremovable media data storage units 240.1.1 which has been connected tochannels B and C from the second level removable media data storagesystem controller 220.

[0069] Shown in FIG. 5 is a third embodiment 300 of the cascaded tapedata storage system of the present invention. The reference numbers forsimilar components are the same as in the previous embodiments; however,a numeral “3” has been added to the reference numbers in the hundredsplace. The third embodiment 300 is distinguishable from the secondembodiment 200 in that an additional set of removable media data storageunits 340.2.1 has been added to the right side 300E of the cascade 300.The additional set of removable media data storage units 340.2.1 isattached to channels C and D from the second level removable mediastorage data system controller 330.

[0070] The fourth embodiment 400 of the invention is depicted in FIG. 6.Similar components having a similar location in the system aredesignated by the same reference numerals with the exception of anumeral “4” in the hundreds place. In this fourth embodiment 400, athird mirrored cascade 400B of removable media data storage units 440.3is added at channel B from the first level removable media data storagesystem controller 410. Accordingly, there are three sets of removablemedia data storage units 440.1, 440.2 and 440.3 connected through secondlevel removable media data storage system controllers 420, 430 and 450to the first level removable media data storage system controller 410.

[0071] Depicted in FIG. 7 is a fifth embodiment 500 of the cascadedremovable media data storage system of the present invention. Similarcomponents having similar positions within the system are designated bysimilar reference numbers with the exception of a “5” in the hundredsplace. The difference between the fifth embodiment 500 and the priorembodiments is the same as the difference between the embodiment 200shown in FIG. 4 and the basic system 100 shown in FIG. 3. Specifically,an additional set of removable media data storage units 540.3.1 has beenadded to a mirrored cascade 500B of removable media data storage unitsconnected to channel B of the first level removable media data storagesystem controller 510.

[0072] Shown in FIG. 8 is a sixth embodiment 600 of the cascadedremovable media data storage system of the present invention. Similarcomponents having a similar position within the system are designated bythe same reference numbers except for the addition of a “6” in thehundreds place. In the sixth embodiment 600, a fourth mirrored cascade600D of removable media data storage units is connected to channel D onthe first level removable media data storage system controller 610. Likethe other branches, the fourth mirrored cascade 600D of removable mediadata storage units 640.4 includes a second level removable media datastorage system controller 660 and removable media data storage units 640connected to channel D of the first level removable media data storagesystem controller 610.

[0073] A seventh embodiment 700 of the present invention is shown inFIG. 9. Similar components having a similar position within the cascadedsystem are designated by similar reference numbers with the exception ofthe number “7” in the hundreds place. The embodiment 700 shown in FIG. 9is similar to the embodiment 600 shown in FIG. 8 in that there are foursecond level removable media data storage system controllers 720, 730,750, and 760 which are connected to four of the five channels A, B, Dand E on the first level removable media data storage system controller710. Much like the fifth embodiment 500 shown in FIG. 7, an additionalset of removable media data storage units 740.3.1 has been added to theadditional branch 700B connected to channel B on the first levelremovable media data storage system controller 710.

[0074] Shown in FIG. 10 is an eighth embodiment 800 of the system of thepresent invention. Similar reference numbers have been used to designatesimilar components in a similar location within the system with theexception of the numeral “8” appearing in the hundreds place. Much likethe seventh embodiment 700 shown in FIG. 9 differs from the sixthembodiment 600 shown in FIG. 8 by the addition of extra removable mediadata storage units to one mirrored group of removable media data storageunits branch 700B of the cascaded system 700, the eighth embodiment 800differs from the seventh embodiment 700 shown in FIG. 9 by the additionof a second set of removable media data storage units 840.4.1 to anothermirrored cascade 800D of removable media data storage units in thecascaded system 800.

[0075] Shown in FIG. 11 is a ninth embodiment 900 of the cascadedremovable media data storage system of the present invention. Similarcomponents having similar locations within the system 900 have beendesignated by similar reference numbers as in the prior embodiments withthe exception of a “9” in the hundreds place. The ninth embodiment 900of the cascaded 900C system of the present invention differs from priorembodiments in that a fifth mirrored cascade of removable media datastorage units 940.5 extends from channel C in the first level removablemedia data storage system controller 910. This branch includes a secondlevel removable media data storage system controller 970 and removablemedia data storage units 940.5 as in the other mirrored cascades ofremovable media data storage units.

[0076] Shown in FIG. 12 is a tenth embodiment 1000 of the instantinvention. Similar reference numbers have been used with similarcomponents having a similar position within the system with theexception of a “10” in the hundreds place. The tenth embodiment 1000 issimilar to the ninth embodiment 900 shown in FIG. 11 in that there are 5mirrored cascades of removable media data storage units 1040A, 1040B,1040C, 1040D and 1040E connected to the first level removable media datastorage system controller 1010. The data storage capacity of thisembodiment 1000 has been increased over the ninth embodiment 900 shownin FIG. 11 by adding additional removable media data storage units1040.3.1 connected to the second level removable media data storagesystem controller 1050.

[0077] The eleventh embodiment 1100 of the cascaded data storage systemof the present invention is shown in FIG. 13. Similar reference numbershave been given to similar components having a similar location withinthe cascaded data storage system; however, the numeral “11” has beenplaced in the hundreds place. Just as additional removable media datastorage capacity 1040.3.1 has been added to the mirrored cascade ofremovable media data storage units 1040.3 connected to second levelremovable media data storage system controller 1050 in the tenthembodiment 1000, additional removable media data storage units 1140.1have been added to the mirrored cascade of removable media data storageunits connected to the second level removable media data storage systemcontroller 1160 in the eleventh embodiment 1100.

[0078] Shown in FIG. 14 is a twelfth embodiment 1200 of the cascadedsystem of the present invention. Similar reference numbers have beenused to identify similar components as in the prior embodiments with theaddition of numeral “12” in the hundreds place. Much like additionalremovable media data storage units 1030.3.1 and 1140.4.1 have been addedto mirrored cascades 1000B, 1100D of the cascaded data storage system inthe prior two embodiments 1000, 1100, the embodiment 1200 illustrated inFIG. 14 adds additional removable media data storage units 1240.5.1 to athird mirrored cascade 1200 of removable media data storage units1240.5.

[0079] It will be understood by those of ordinary skill in the art thatit is possible to add additional removable media data storage units toeach one of the second level removable media data storage systemcontrollers. If desired, however, the open channels on each second levelremovable media data storage system controller may be attached to avariety of different data storage devices provided the data storagedevices can adequately receive commands from the second level removablemedia data storage system controllers.

[0080] While the preferred and several alternate embodiments of theinstant invention have been described above, those of ordinary skill inthe art will understand that still other embodiments of the instantinvention are possible once having understood the foregoing disclosure.Such other embodiments shall be included within the scope and meaning ofthe appended claims.

What is claimed is:
 1. An enhanced removable media data storage system controller portion connected to one or more individual removable media data storage units for back-up storage of data from a host computer, said enhanced removable media data storage system controller comprising: means for virtualizing functionality commands from a host computer to a robotic control of one or more removable media data storage units; means for virtualizing status commands from the robotic control of one or more removable media data storage units to a host computer; means for creating a path for data travel to a mirrored group of one or more removable media data storage units.
 2. The enhanced removable media data storage system controller as defined in claim 1 wherein said removable media data storage system controller has five channels.
 3. An enhanced removable media data storage system controller portion of removable media data storage unit for back-up storage of data from a host computer, said improved removable media data storage system controller comprising: means for virtualizing functionality commands from a host computer to a robotic control of one or more removable media data storage units; means for virtualizing status commands from the robotic control of one or more removable media data storage units to a host computer; means for creating a path for data travel to either a mirrored group of one or more removable media data storage units or a 2+1 RAID.
 4. The enhanced removable media data storage system controller as defined in claim 3 wherein said 2+1 RAID includes one or more removable media data storage units.
 5. The enhanced removable media data storage system controller as defined in claim 3 wherein said improved removable media data storage system controller has five channels.
 6. A cascaded removable media data storage system comprising: a first level removable media data storage system controller; at least two second level removable media data storage system controllers connected in parallel to said first level removable media data storage system controller; one or more removable media data storage units connected to each of said at least two second level removable media data storage system controllers; each of said second level removable media data storage system controllers including: means for being aware of the other removable media data storage system controllers in the cascaded removable media data storage system; means for virtualizing functionality commands from a host computer to a robotic control of one or more removable media data storage units; means for virtualizing status commands from the robotic control of one or more removable media data storage units to a host computer; means for creating a path for data travel to a mirrored group of one or more removable media data storage units.
 7. The cascaded removable media data storage system as defined in claim 6 wherein each of said removable media data storage system controllers has five channels.
 8. A cascaded removable media data storage system comprising: a first level removable media data storage system controller; at least two second level removable media data storage system controllers connected in parallel to said first level removable media data storage system controller; one or more removable media data storage units connected to each of said at least two second level removable media data storage system controllers; each of said removable media data storage system controllers including: means for being aware of other removable media data storage system controllers in the cascaded removable media data storage system; means for virtualizing functionality commands from a host computer to a robotic control of one or more removable media data storage units; means for virtualizing status commands from the robotic control of one or more removable media data storage units to a host computer; means for creating a path for data travel to a mirrored group of one or more removable media data storage units or a 2+1 RAID.
 9. The cascaded removable media data storage system as defined in claim 8 wherein said 2+1 RAID includes one or more removable media data storage units.
 10. The cascaded removable media data storage system as defined in claim 8 where each of said removable media data storage system controllers has five channels.
 11. The cascaded removable media data storage system as defined in claim 6 wherein said first level removable media data storage system controller which is connected to at least two second level removable media data storage system controllers further includes at least one additional second level removable media data storage system controller connected to one of said at least two second level removable media data storage system controllers.
 12. The cascaded removable media data storage system as defined in claim 8 wherein said first level removable media data storage system controller which is connected to at least two second level removable media data storage system controllers further includes at least one second level removable media data storage system controller connected to at least one of said second level removable media data storage system controllers.
 13. A computer network comprising: at least one host computer; said at least one host computer connected to a cascaded removable media data storage system; said cascaded removable media data storage system including: a first level removable media data storage system controller; at least two second level removable media data storage system controllers connected in parallel to said first level removable media data storage system controller; one or more removable media data storage units connected to each of said at least two second level removable media data storage system controllers; each of said second level removable media data storage system controllers further including: means for being aware of other removable media data storage system controllers in said cascaded removable media data storage system; means for virtualizing functionality commands from a host computer to a robotic control of said one or more removable media data storage units; means for virtualizing status commands from the robotic control of said one or more removable media data storage units to said at least one host computer; means for creating a path for data travel to a mirrored group of one or more removable media data storage units.
 14. The computer network as defined in claim 13 where in each of said removable media data storage system controllers has five channels.
 15. A computer network comprising: at least one host computer; said at least one host computer connected to a cascaded removable media data storage; said cascaded removable media data storage system including: a first level removable media data storage system controller; at least two second level removable media data storage system controllers connected in parallel to said first level removable media data storage system controller; one or more removable media data storage units connected to each of said at least two second level removable media data storage system controllers; each of said second level removable media data storage system controllers further including: means for being aware of other removable media data storage system controllers in the cascaded removable media data storage system; means for virtualizing functionality commands from said at least one host computer to a robotic control of said one or more removable media data storage units; means for virtualizing status commands from the robotic controller portion of said one or more removable media data storage units to said at least one host computer; means for creating a path for data travel to either a mirrored group of one or more removable media data storage units or a 2+1 RAID.
 16. The computer network as defined in claim 15 wherein said 2+1 RAID includes one or more removable media data storage units.
 17. The computer network as defined in claim 15 wherein each of said removable media data storage system controllers has five channels.
 18. The computer network as defined in claim 13 wherein said first level removable media data storage system controller which is connected to at least two second level removable media data storage system controllers further includes as least one second level removable media data storage system controller connected to one of said at least two second level removable media data storage system controllers.
 19. The computer network as defined in claim 16 wherein said first level removable media data storage controller connected to at least two second level removable media data storage system controllers further includes at least one second level removable media data storage system controller connected to one of said at least two of said second level removable media data storage system controllers. 